This invention relates to a semiconductor photocathode, formed using a semiconductor as a component material, and which is excited by incident light and emits photoelectrons.
Conventional semiconductor photocathodes for use with ultraviolet light were formed for example from AlxGa1-xN. Preexisting technology related to such semiconductor photocathodes formed from AlxGa1-xN is disclosed in the specification of U.S. Pat. No. 5,557,167, the specification of U.S. Pat. No. 4,616,248, and in Japanese Patent Laid-open No. 08-96705. Conventional semiconductor photocathodes formed from AlxGa1-xN have a quantum efficiency sufficient to enable practical application in the ultraviolet light.
However, when an attempt is made to perform precise measurements, the quantum efficiency of such conventional semiconductor cathodes cannot be described as sufficient, and AlxGa1-xN system semiconductor photocathodes with still higher quantum efficiencies are desired. The present invention is intended to resolve this problem, and has as an object the provision of a semiconductor photocathode with high quantum efficiency, having an optical absorption layer formed from AlxGa1-xN (0xe2x89xa6xxe2x89xa61).
Upon conducting advanced studies and research to improve the quantum efficiency of this type of semiconductor photocathode, the inventors discovered that the quantum efficiency depends heavily on the content concentration of Mg in the AlxGa1-xN layer (0xe2x89xa6xxe2x89xa61) which is the optical absorption layer.
This invention is a semiconductor photocathode which is excited by incident light and emits photoelectrons, and is characterized in that an optical absorption layer which absorbs incident light and causes the generation of photoelectrons is formed from an AlxGa1-xN layer (0xe2x89xa6xxe2x89xa61) with an Mg content concentration of 2xc3x971019 cmxe2x88x923 or higher and 1xc3x971020 cmxe2x88x923 or less. In this case, the quantum efficiency can be improved over that of the prior art.
Further, this invention is characterized in that the AlxGa1-xN layer forming the optical absorption layer has a composition ratio x of 0.3xe2x89xa6xxe2x89xa60.4. Through such a configuration, a so-called solar-blind type semiconductor photocathode can be realized.